Electrical Service Load Calculator
Size a dwelling's electrical service with the NEC 220.82 optional method. Totals lighting, circuits, and appliances, then suggests a 100, 150, or 200 A panel.
Frequently Asked Questions about the Electrical Service Load Calculator
What is the NEC 220.82 optional method?
It is a simplified way the National Electrical Code lets you size the service for a single dwelling. You add up general loads (lighting at 3 VA per square foot, the required small-appliance and laundry circuits, and the nameplate ratings of fixed appliances), apply a demand factor, then add the larger of your heating or cooling load. It is allowed for a dwelling on a single 120/240 V or 120/208 V 3-wire service rated 100 A or more.
How does the demand factor work?
Under NEC 220.82(C) you take the first 10,000 VA of the combined general load at 100 percent, then the remainder above 10,000 VA at 40 percent. For example, a 34,100 VA general load becomes 10,000 plus 40 percent of 24,100 (9,640), for a general demand of 19,640 VA. The heating or cooling load is added after this and is not discounted by the 40 percent factor.
Why do you use the larger of heating or cooling instead of both?
A home rarely runs full heating and full air conditioning at the same time, so NEC 220.82(C) tells you to count only the larger of the two. This calculator takes 100 percent of the air-conditioning nameplate for cooling, applies the matching factor to your heating type (for example 65 percent for electric space heat with fewer than four units, or 100 percent of a heat pump compressor plus 65 percent of supplemental strip heat), and keeps whichever is bigger.
How do I convert the total to amps and a service size?
Divide the total calculated load in VA by 240 volts to get the demand current in amps. The calculator then snaps that current up to the next standard service rating, such as 100, 125, 150, 200, 225, 300, or 400 A. A load of 26,140 VA is 108.9 A, which calls for a 125 A service.
What counts as the general loads in 220.82(B)?
General loads are 3 VA per square foot of conditioned floor area for lighting and general receptacles, 1,500 VA for each required small-appliance branch circuit (at least two), 1,500 VA for each laundry circuit (at least one), and the nameplate ratings of fixed appliances like the range, oven, water heater, dryer, dishwasher, and disposal. Enter the nameplate VA from each appliance's data plate.
Is this calculator enough to pull a permit?
No. This is a planning estimate to help you understand whether your panel has room for a new load such as an EV charger or a heat pump. The actual service calculation must be performed and signed off by a licensed electrician and approved by your local authority having jurisdiction, who may apply local amendments to the NEC.
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